The aim of the proposed research is to pursue the work initiated to clarify the mechanism(s) involved in the influence of thyroid hormones in brain development. Particular emphasis will be given to membranogenesis, for regardless of the level at which thyroid hormones act, their effects on membrane formation and membrane properties may represent the most important developmental abnormality, at least in terms of the repercussions on functional and behavioral aspects. Specialized brain membranes from control, hypo and hyperthyroid animals will be studied in terms of composition of enzymes, lipid and proteins, as well as in terms of affinity for thyroid hormones and binding properties and various stages of brain development.